Dendrimers are an understudied class of nanometer-scale, globular polymers that offer candidates for the next-generation of polymer therapeutics. Size, shape, and composition impact all aspects of these vehicles including overall efficacy, bioavailability, toxicity, metabolism, absorption and excretion. Optimization of these parameters for drug delivery using dendrimers requires (1) exquisite control over the synthesis of dendrimer candidates; (2) an understanding of the physical organic chemistry of these macromolecules and macromolecule-drug complexes; and finally, (3) assessment of therapeutic efficacy. To date, owing to synthetic routes that lack an approach for systematic variation of size, shape, and composition as well as number of architectures for structure-property relationships (the hallmark of physical organic chemistry), there is little fundamental understanding of the design criteria for the use of dendrimers in drug delivery. There are three overall aims of proposed research which focuses on breast and prostate tumors: Specific Aim #1: Examine the fundamental physical organic chemistry of these macromolecules as it pertains to: 1 A) The number of "phases" a biocompatible PEGylated dendrimer comprises in water and the impact that this has on the sequestration of drugs: In monophasic dendrimers, sequestration is proportional to MW. 1B) The ability to tailor release rates of drugs through systematic cleavage of bioloabile linkers in architectures showing a gradient of tethers and steric crowding. 1C) The global conformation of these macromolecules and the guests associated with them. Specific Aim #2: Identify the molecular determinants for biodistribution and tumor targeting using multifuctional dendrimers. Specific Aim #3: Explore macromolecular recognition to determine the molecular parameters that allow these dendrimers to serve as synthetic vaccines and as multi-functional adaptor units on antibodies.